In some standard implementations of communication protocols such as 3GPP, e.g. in Rel-10, established dedicated bearers are deactivated by a mobility management entity (MME) in case of an S1-release due to loss of radio connection; the deactivation of bearers are specified for Guaranteed Bit Rate (GBR) bearers but not for non-GBR bearers, i.e. best effort bearers. The deactivation of these bearers will be notified to a packet data network gateway (PDN GW or PGW) that will remove policy and charging control (PCC) Rules bound to the removed bearer(s) and then notify an application function (AF) via a Policy and Charging Rules Function (PCRF) that no resources are available for the call/session which will cause the application function (AF) to terminate ongoing calls/sessions for that user equipment (UE). One example of an AF is a Proxy Call Session Control Function (P-CSCF) which is a border control unit of an IP multimedia Core Network (IM CN) subsystem.
At a later stage the UE may recover radio coverage or resume connection in any other way and the UE will then try to establish new calls that will cause the AF to request resources over an Rx interface, the PCRF generates PCC Rules, installs them in a policy and charging enforcement function (PCEF) and this will trigger establishment of dedicated bearer to transfer the associated media for the call/session.
If the UE regain coverage while the user still attempts to communicate with the remote party, then the UE may try to send user data through bearers that allow such traffic i.e. typically best effort bearers that did not got deactivated while the UE was out of coverage. However, as the PCC rules got removed and the AF session was terminated the only way for the user to continue the communication with a remote party is to initiate a new call to the same remote party. However, it is possible to continue communication using a non-GBR quality of service if there is a policy and charging control (PCC) rule, but for re-establishment of communication with respective dedicated QoS service(s) needs to be set up again.
In Release 11 of the 3GPP standard, there is a proposal to preserve the dedicated bearer in case of an S1-release due to loss of radio connection and notify the AF to be able to reject new incoming calls to the UE. This can be found in 3GPP TS 23.203 v. 11.1.0 discussing policy and charging control architecture and more information about the procedures related to this may also be found in TS 23.401 v. 10.3.0 discussing General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access.
The network deactivates dedicated bearers for GBR related bearers, when the UE is out of coverage, this will cause release of ongoing calls and the user/UE needs to initiate the calls from scratch that will be re-established when the UE regain communication coverage.
Even when the UE may regain communication coverage within a short period of time, the calls have already been released, and thus calls will have to be reinitiated.